The present invention relates to power units used to drive manually-operated conventional wheelchairs, and more particularly, to novel power units which are attachable to and detachable from conventional wheelchairs for producing power-driven wheelchairs.
Conventional manual-powered wheelchairs of varying configuration are well-known in the prior art. Furthermore, power-driven wheelchairs, particularly electrical power driven wheelchairs, are also known in the prior art. Unfortunately, many people who require the use of a powered wheelchair are not able to afford one because they are too expensive for them to purchase. Therefore, an aftermarket has developed for detachable electrical drive power units for conventional non-powered wheelchairs. But even these latter detachable power units are in the several thousand dollar price range and have significant design limitations.
Various types of these detachable drive units are known in the prior art. For example, U.S. Pat. No. 4,386,672 comprises such a unit mounted under the front of the wheelchair with the steering column extending upward from the front center of the wheelchair between the legs of the wheelchair occupant. This handle is supported to a swivel by means of a lower cooperating joint so that a person can get in and out. First of all, it is impractical for a disabled person to try to get in and out of a wheelchair having an obstruction in the front of same. This is the case even here where the handle swings out of the way since one can still stumble over it. Once seated in the chair, it becomes difficult for the user to reach the handle in its retracted position. Additionally, there is no way of preventing the handle from falling over when the user wants to move the handle out of the way or to a retracted position. If the handle were secured at a higher level, to expedite use by a person sitting in the wheelchair, this would interfere with the entry and exit from the wheelchair by the user. Finally, the handle U-joint arrangement provides for difficulty in handling of the steering for a person sitting in the chair because of the amount of strength required to maneuver the chair with this type of direct-drive configuration.
U.S. Pat. No. 2,495,573 comprises a motor attachment for wheelchairs which is large, bulky, not easily attached to or removed from a conventional wheelchair, and difficult to transport in a vehicle. The steering is located at the front of the wheelchair and includes casters. If the steering wheels are lifted up off the ground, steering is eliminated. The rear wheels, which are belt driven, are not directly driven but instead follow the turning operations of the device.
U.S. Pat. No. 4,759,418 describes an electrical drive attachment for a wheelchair. The drive is not reversible because of the contact angle between the drive device and the ground as hereinafter described. This provides for poor steering. Because of its location behind the rear axle it will resist efforts to turn. Since the angle of contact of the wheels with respect to the ground is about 70% in order to maintain good traction, any surface irregularities will be magnified many times, resulting in an erratic drive pattern. Furthermore, since the drive wheel is not in alignment with the rear wheels, a user of the wheelchair must skid one side or the other to turn the unit.
U.S. Pat. No. 2,993,550 comprises a multi-wheel, multi-motor unit. This unit is difficult to assemble, disassemble, and transport by vehicle. The steering mechanism turns the front wheels so that the problems described above with respect to U.S. Pat. No. 4,386,672 are applicable herein.
U.S. Pat. No. 3,688,857 and U.S. Pat. No. 3,100,547 each have two motors and include drive belt assemblies attached to a battery and stand, making it quite bulky and difficult to use for transport. This unit provides variable speed steering by the counteracting effect of two motors used in tandem. This type of maneuvering of the chair is particularly difficult for handicapped persons who are trying to drive the wheelchair. In the case of U.S. Pat. No. 3,100,547, the unit includes a battery trailer with one caster wheel.
U.S. Pat. No. 2,978,053 is a driving and steering apparatus for wheelchairs. It includes a cart for the wheelchair and is tilted back in use which creates a very unstable condition for the driver. It also includes multi-wheels and multi-motors. The unit has front wheel drive and steering. Suffice it to say, this unit is heavy, bulky, and difficult to assemble, disassemble, and store in vehicular use for trips.
Examples of motorized invalid vehicles which are not adapted for use in conjunction with conventional wheelchairs, but are instead manufactured for direct power-driven use, are set forth in U.S. Pat. No. 3,896,891 ("Modular Motorized Wheelchair"), U.S. Pat. No. 3,770,073 ("Foldable Invalid Chair"), and U.S. Pat. No. 4,750,578 ("Dismantleable and Collapsible Utility Cart").
Therefore, a need exists for a motorized unit for driving a conventional wheelchair which overcomes the problems described above with respect to the prior art devices.